Wing tip tank construction



June 15, 1954 c. E. PAPPAS WING TIP TANK CONSTRUCTION Filed April 7. 1950 ATTORNEY.

Patented June 15, 1954 g UNITED STATES ATENT OFFICE WING TIP TANK CONSTRUCTION Costas E. Pappas, Huntington, N. Y., assignor to Republic Aviation Corporation, Farmingdale, N. Y., a corporation of Delaware Application April 7, 1950, Serial No. 154,487 6 Claims. (Cl. 244-135) This invention relates generally to bodies havthese unstable conditions occasioned by the ing aerodynamic shapes or contours, such as fuel mounting of a tank at or on a wing tip that the cells or tanks, which are to be externally mounted present invention is addressed on, or are to be carried by, a component of an When a tank or other body is mounted on, or airplane, such as a wing, and has for one of its 5 carried at the end or tip of an airplane Wing, objects the provision of means to counteract or whether immediately under or surrounding or prevent any adverse effect on the stability of the embracing the wing tip, it has been found that in airplane, or of a component thereof, that may be maneuvers involving changes in attitude of the occasioned by, or result from, so mounting such airplane, such as in climb or descent, the nose or body thereon. l0 forebody of the tank tends to continue any dis- Primarily the instant invention is concerned placing movement resulting from a change in the with the installation or mounting of tanks ha-vangle of attack or of the attitude of the airplane ing aerodynamic shapes or contours at, or imand necessarily of its wings. Thus a tank situated mediately adjoining, the outboard ends or tips of at a wing tip is, or becomes, an unstable body, the wings of an airplane and proposes to incorposince, when displaced, it tends to continue its disrate in, or associated with, the tank structure placing movement rather than tends to return to means that will aerodynamically react with the its original or neutral position upon the disconairstream to stabilize the tank relatively to the tinuance of the displacing moment; as would be wing and prevent it from adversely affecting the the case with a stable body.

stability not only of the wing to which it is at 90 In short, the nose of a tank during maneuvers tached but that of the airplane as well. tends to continue any movement, either up or With the above and other objects in View this down, resulting from a change in the angle of invention consists in the construction, combinaattack or attitude of the airplane after this tion and arrangement of parts, all as hereinafter change has been completed. This tendency on more fully described, claimed and illustrated in 25 the part of the tank causes the wing to twist or the drawings wherein: distort and this twisting of the wing destroys or Fig. 1 is a plan view of a tank, embodying the greatly reduces the stability of the wing and of present invention, showing it in association with, the airplane. When the tank is full the resulting or mounted on, the tip of an airplane wing; twisting movement of the wing is present but is Fig. 2 is a transverse section taken through the 1 of less magnitude. aft end of the tank along line 22 of Fig. 1; and It is recognized that an unstable body of revo- Fig. 3 is a section taken along line 3-3 of Fig. lution tends to continue its angular displacement 1 to illustrate the aerodynamic shape or profile from neutral; thus if the angle of attack of the of the fin associated with or carried by the aft end body is increased or decreased, the body tends to of the tank as taught by this invention. continue such increase or decrease rather than To increase the range or radius of action of an return to its original position as would be the case airplane it has become more or less common pracwere it an entirely stable body. A wing tip tank tice to mount external fuel tanks on various comis an unstable body of revolution and, due to its ponents of the airplane and this means of inposition, as the angle of attack of the airplane is creasing operational range is particularly useful changed the tank tends to continue its movein military aircraft. These tanks on occasion ment caused by such change, or to amplify the have been mounted under the fuselage, but more degree of change, with the result that the wing is generally have been mounted under the wings twisted and distorted, sometimes to the point of inboard of the wing tips and not infrequently disintegration. The tank thus being an unstable nearer to the root ends of the wings than to their 55 body contributes appreciably to the instability of tips. Recently it has been found more practical the entire airplane.

and desirable to mount such auxiliary or external The present invention proposes to aerodynamfuel tanks at the wing tips. In some instances, ically overcome the instability of a tank situated the tank has been mounted immediately under at the tip of a wing by incorporating a fin on the Wing tip while in others it has been mounted so the outboard side or surface of the tank, which at and surrounding or embracing the wing tip, in and of itself constitutes a symmetrical airfoil and in either case so positioning the tank defixedly secured to the tank, and preferably having velops problems of stability in relation not only a contour or profile or" the same order as that of to thewing but also relative to the overall stabilthe wing that carries the tank. This fin is posiity of the airplane. It is to the correction of 55 tioned substantially in the plane of the Wing carrying the tank, or parallel thereto, and being outboard of the extremity of the wing is not noticeably affected by the turbulence of air spilling or flowing off the wing.

The placing of a fin on the outboard surface of a tip tank serves two purposes. First, it eliminates the instability which would occur with a tank not having a fin. The aerodynamic stability resulting from mounting a tank with a fin at the tip of the wing permits the pilot to more easily change the attitude of the airplane. Thus, as an airplane having neutral stability requires practically no stick force on the part of the pilot to effect a maneuver, so may the pilot easily overcontrol the airplane during a maneuver and this results in excessive load factors on the airplane. By incorporating a fin on the tank as aforesaid, the unstable moments of the basic body can not only be reduced, but the body itself can be made stable. Thus the overall stability of the airplane can be increased. Second, the installation of a fin as aforesaid reduces the twist and distortion of the wing since the unstable aerodynamic moments can be reduced materially, if not eliminated, by the use of the fin. aerodynamic moment, as herein used, is meant the tendency of the wing tip tank to rotate on its point of attachment to the wing tip due to the pressure distribution of air loads on the tank itself. The wing reacts to thereby introducing a wing.

Reference being had more particularly to the drawings, if! designates the tip of an airplane wing with which a fuel tank ii is associated by having the wing tip is received in a pocket or recess i2 formed in the inboard surface or wall of the tank. In most installations the nose l3 of the tank is situated forward of the center of gravity of the airplane while the aft end i l thereof is positioned thereof. Any suitable means Hm is employed to attach the tank H to the wing tip it but since this means forms no part of the instant invention it is shown sche matically in Fig. 1. It is sufficient to note that the tank H is attached to the wing ill by any suitable means lea located within the confines of the pocket or recess 12.

The present invention resides in xedly mounttwist or distortion in the ing a fin to at the aft end of the tank ii on the outboard surface thereof, i. e., in opposition to the wing tip it. This fin 55 may be of any adaptable construction and preferably consists of a metal sheet bent upon itself to create the leading edge 65, the trailing edge ii, the upper surface it and lower surface It". In the illustrated adaptation of this invention the surfaces l5 and 55" of the fin l5 converge rearwardly to where two of the edges of the sheet forming the fin it are superposed and secured together to constitute the trailing edge l2. The profile (Fig. 3) of the fin is is a true airfoil and while this is not an essential requirement, it is preferred that it be of the same order as the profile of wing ill to which the tank i l is to be attached.

This fin I5 is mounted on or against the outboard surface of the aft end E5. of the tank H with its trailing edge if normal to the longitudinal axis of the tank and in transverse alignment with the rear or aft extremity of the tank. When the fin is so positioned the leading edge l6 thereof slopes outwardly and aftwardly from a point on the outboard surface of the tank I l forward of the rear or aft extremity thereof. to the outer end of the trailing edge l1. Adjacent the this aerodynamic movement tank I l the inner edges l8 of the upper and lower surfaces l5 and i5 (Fig. 2) of the fin l5 are superposed and spaced one from the other and are arranged to abut fiush against the outboard surface of the tank throughout their length, i. e., from the rear extremity of the tank to the inner or forward extremity of the leading edge l6.

These edges It may be fixedly and rigidly secured to the tank in any manner and one example of this attachment is disclosed herein. A reinforcing plate 19, shaped to conform to the curvature of the tank wall, is placed flush against the inner face of the wall and is more than coextensive with the space defined by or between the edges l8 of the fin located against the outer surface of the tank wall at that point. Angle bars 20 positioned within. the space defined by the upper surface it and lower surface E5" of the fin at and underlying the edges is thereof, have one arm 20' of each secured at spaced intervals to the wall of the tank and to the internal reinforcing plate H?) by any means, such as the rivets 2i. The remaining arms 2% of the angle bars 20 underlie and rest fiush against the inner faces of the edge portions it of the upper and lower surfaces l5 and i5 of the fin to be rigidly and fixedly secured thereto at spaced intervals by any suitable attaching means, such as the rivets 22.

It is evident that when the tank is is mounted on the wing tip iii as shown in 1, the fin l5 being onthe outboard side of the tank is thereby positioned appreciably outboard of the end of the wing. If the tank H is mounted directly under the wing tip it, the fin it being associated with the outboard. surface of the tank will be positioned and project beyond the wing tip. In either case the fin 15, being located beyond the wing tip ill, will not be affected by the turbulence of air spilling or flowing off the wing.

What is claimed is:

l. The combination with an elongated body having an aerodynamic contour and organized and arranged to be attached medially of its length to the outer end of the wing of an airplane, of

a single fin comprising the sole stabilizing means on said body and having leading and trailing edges and the profile of an airfoil, fixedly secured to and projecting from the outboard side only of said body, with its trailing edge normal to the longitudinal axis of the body.

2. A tank having means at one side thereof adapted for mounting said tank to the tip of an airplane wing, said tank comprising a hollow body of aerodynamic contour, and a single fin comprising the sole stabilizing means on said tank and fixedly secured to the side of the body op- V posite to said mounting means to project outwardly therefrom.

3. A tank comprising an elongated body having means at one side thereof adapted for mounting said tank to the tip of an airplane wing, and a single fin comprising the sole stabilizing means on said tank and including a leading and a trailing edge, fixedly secured and to projecting from one end of said body at the outboard side only thereof with its trailing edge positioned normal to the longitudinal axis of the body and in transverse alignment with the aft extremity of the body.

4. A tank comprising an elongated body having means at one side thereof adapted for mounting said tank to the wing tip of an airplane and a single fin comprising the sole stabilizing means on said tank,,including, a leading and a trailing edge, fixedly secured to one end of the body at the out- 5 board side only thereof with its trailing edge disposed normal to the longitudinal axis of the body and in transverse alignment with the aft extremity thereof and its leading edge angularly disposed between the wall of the body and the outer end of the trailing edge.

5. The combination with the wing of an airplane, of an aerodynamic body attached to the tip thereof, and a single fin comprising the sole stabilizing means on said body fixedly secured to and projecting from the aft end of said body and at the outboard side only of its longitudinal axis.

6. The combination with the wing of an airplane, of an aerodynamic body associated medially of its length with the tip thereof and a single fin comprising the sole stabilizing means on said body secured to and projecting from the aft end of the outboard side only of said body.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,749,047 St. Louis Mar. 4, 1930 2,273,919 Allw'ard Feb. 24, 1942 2,326,819 Berlin Aug. 17, 1943 2,417,342 Bach Mar. 11, 1947 2,537,369 Astroff Jan. 9, 1951 FOREIGN PATENTS Number Country Date 606,088 Great Britain Aug. 5, 1948 872,789 France Feb. 23, 1942 923,549 France Feb. 24, 1947 

